Fossils are the remains of an animal or creature that lived a really long time ago.A fossil is formed when a creature dies ,after the creature is dead other animals come and eat the remaining flesh.Next the creatures bones become covered with more and more layers of sand .After hundreds of years the bones gradually get covered with more sand,the water and sand eventually replace the chemicals with minerals and after a long period of time the movement of the earth brings the fossil up in the earth until someone dig it up.